hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 1, 2019 16:12:02 GMT -5
Just finished drawing up a flame tube design and am looking for a sanity check. Tube OD is 5" by 13" long. Side questions: Would it help if the holes were cut so they have ~45 degree funnel shape? I was thinking that if this was done, it would create a smoother stream of air as its injected and mixed with fuel. How about if the holes were cut so they point up or down?
|
|
|
Post by racket on Dec 1, 2019 16:48:35 GMT -5
Plain holes are OK , no need to go "fancy" , placement is more important , and your current design has me "concerned" , .... those Primary holes at the top , how have you determined their position and number ??
Cheers John
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 1, 2019 18:45:26 GMT -5
Plain holes are OK , no need to go "fancy" , placement is more important , and your current design has me "concerned" , .... those Primary holes at the top , how have you determined their position and number ?? Cheers John Hi John, I based their number and size on jetspecs. My positioning of the primary holes is based on the picture in Jetspecs and how I did it last time. I moved them from 1.6 to 1.0 inches from the top thinking it would move the flame higher and perhaps easier to start with the spark plug closer. Jetspecs does not seem to give an offset value. The nozzle is long enough so I can offset the holes by up to 2.5 inches from the top. Is there a better way to determine this offset? The secondary and tertiary positions were based on the Jetspecs pic as well, right in the middle.
|
|
|
Post by racket on Dec 1, 2019 19:38:58 GMT -5
Jetspecs assumes?? that propane is the fuel with regards the Primary hole configuration , the radial jets of propane mix with the air coming through the multitude of smallish holes , and as propane is very forgiving with regards mixture strength ( A/F ratio) and burns quickly , virtually any arrangement will work .
But for liquid fuels we need to be a tad more sophisticated with our hole positioning and number depending on how the fuel is being fed into the engine . .....................I'm having difficulty following your build as the Thread is being broken up into sub threads and I'm not certain what relates to what :-(
Could you please clarify your fueling method/type etc
Cheers John
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 1, 2019 21:09:04 GMT -5
I'm sorry about the confusion caused by multiple threads. I thought I was doing the right thing by separating the individual topics instead of a long rambling thread. I was unaware that jetspecs assumes propane.
My starting message should have included "Holset 3522950, Inducer diameter: 55mm (opening is 95mm and funnels down to 55mm), Exducer diameter: 75mm"
Short term goal: For now, start and run on propane. Use this time to work out details on instrumentation and quirks of the engine. Learn how to have consistent and reliable operation. If possible, design combustor so swapping head flange is all it takes to change fuel.
Long term goal: Run on oil, maybe propane start. Exhaust nozzle.
Very long term goal: Afterburner!!
|
|
|
Post by racket on Dec 1, 2019 22:04:35 GMT -5
LOL........I like long rambling Thread builds , much easier to chase up a solution to a problem . OK , propane now but oil later , so design for oil , the propane will accommodate any "off design" in the flametube .................you'll note that the Jetspecs graphics shows 3 lines of primary holes which would help somewhat with any axial displacement issues of the fuel entry . As the propane injector can be a very crude device, it easy to make it adjustable axially within the flametube for the radial injection pattern to align with oil burning positioning of the main/lower Primary Air row of holes as per my reply jetandturbineowners.proboards.com/thread/1292/kerosene-injector-placement-propane-starterAs your 55mm inducer has an area of 2375 sq mms , the Primary Zone needs 2375 X 0.3 = 712 sq mms , therefore 237 sq mms for the top row of holes and 475 sq mms for the second row of holes positioned where the oil spray would impact the flametube wall , lets use 8 holes at that position , so ~60 sq mms/hole , so ~8.7 mm dia by 8 of, .................the uppermost 8 holes each have an area of ~30 sq mms/hole or ~6.2 mm dia X 8 of. Cheers John
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 8, 2019 13:49:34 GMT -5
How about this? Im considering abandoning the propane start oil run approach and just stick with propane to keep things simple. If I went that route, do you think my original design would work?
|
|
|
Post by racket on Dec 9, 2019 22:48:49 GMT -5
Yep .
Aim the propane for the lower row of Primary holes
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 11, 2019 9:07:54 GMT -5
Then that is what I'll do. Adding and removing holes isn't an issue.
My propane nozzle, I'm planning on reusing the one I already built. It has 6x 3.2mm holes drilled into the 6 faces on the hex head. The hole down the middle is 7mm.
Do you see a problem with this?
I was thinking of machining flats on the 6 points of the head and add 6 more 3.2mm holes. (Total of 12 radial holes) My thinking is that I can get more flow and better coverage of the primary air holes.
|
|
|
Post by racket on Dec 11, 2019 16:15:47 GMT -5
I'd suggest using smaller holes for the radial injection , the 7mm hole has an area of ~39 sq mms , the 6X3.2 mm have ~48 sq mms , you might end up with uneven injection rates , maybe go for 12 X 1/16" and a bigger hole down the centre
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 12, 2019 16:34:57 GMT -5
1/16" holes that deep are a pain but I'm up for a challenge.
|
|
|
Post by racket on Dec 12, 2019 17:36:00 GMT -5
Why not just use a short length of 3/8" tubing with the end crimped/welded over and the 12 holes through the thinner wall section , have a compression fitting in the endcap to allow axial adjustment of the tube/holes to match the FT wall holes
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 13, 2019 12:05:40 GMT -5
That's a really good idea. Never thought of it. I've already started making this one but if I reach a point where I have to start over, that's what I'll do.
|
|
hosedup
Junior Member
Joined: October 2019
Posts: 68
|
Post by hosedup on Dec 15, 2019 11:05:01 GMT -5
Yep . Aim the propane for the lower row of Primary holes I'm confused. I asked about using my original design for propane only and you said to aim for lower holes. But it only had one row of holes, the second design has 2 rows.
|
|
|
Post by racket on Dec 15, 2019 16:08:01 GMT -5
OOPS ..............sorry about the confusion , its just you had the updated flametube design with the question , use the updated design , the upper holes will help cool the cap before entering the combustion phase .
|
|